A reverse DNS lookup that acquires a fully qualified domain name (FQDN) on the basis of an internet protocol (IP) address is described, for example, in Non-Patent Document 1 described below. In FQDN, a domain name is described in a manner that specifies, for example, a domain name, a sub domain name, a hostname, and so on without omission. Hereinafter, the character string, which is information on each communication node and which is described in a specified form such as FQDN, is referred to as a domain name. A communication device performs a reverse DNS lookup using an IP address acquired through a certain method, thereby acquiring a domain name of a communication device identified on the basis of the IP address.